1. Field
One embodiment of the present invention relates to a disk drive able to correct errors in the data recorded in the data-recording area of a disk.
2. Description of the Related Art
In recent years, discrete track media (DTM) disks and patterned media disks such as bit-pattern media (BPM) disks have been attracting attention in the field of disk drives, typically hard disk drives. (See, for example, U.S. Pat. No. 5,956,216.) BPM disks are magnetic disks in which the bits in each track are physically separated from one another.
An ordinary magnetic disk has surface regions made entirely of magnetic material. Hence, data is magnetically recorded on either surface, as a head applies a recording magnetic field to the surface. On the other hand, in the surface of any BPM disk, magnetic dots (processed magnetic dots), which correspond to the bits that constitute the recorded data, are formed, defining a magnetic-dot pattern. Note that the magnetic dots are physically separated from one another and are thus independent of one another.
Any disk drive incorporating a BPM disk allocates one or more magnetic dots to one bit (0 or 1) of the recorded data, thereby magnetically recording the data on the BPM disk. Such a disk drive can enhance the magnetic stability of each bit of data recorded on the disk. This may accomplish high-density data recording, as is expected in this field of the art.
In the disk drive incorporating a BPM disk, however, the head must be accurately positioned relative to the coordinates of each magnetic dot physically processed, at the timing of applying the recording magnetic field. Various methods of controlling the timing of recording have been proposed. (See, for example, Jpn. Pat. Appln. KOKAI Publication No. 2003-281701.)
However, it is difficult to control the timing as desired for all data to be recorded on the disk. If data errors are made because of insufficient timing control, a technique of correcting data errors before reproducing the data from the disk will be important.
The ordinary method performed in conventional disk drives is to record data that includes data to which error-correcting codes (ECCs), such as parity codes, are added, and to correct the errors by using the parity codes at the time of reading the data. (See, for example, Jpn. Pat. Appln. KOKAI Publication No. 2005-252973.)
The conventional method of correcting data errors corrects data-bit errors, i.e., 0s or 1s recorded at the specific data locations in the data-recording area of the disk. This method facilitates the decision of whether the signals at specific data locations are 0s or 1s, if the decision cannot be made otherwise. In brief, the conventional method of correcting data errors is based on the assumption that the total number of data bits that constituting data recorded in a data sector, i.e., one access unit of data, remains unchanged even if this data contains errors.
In any disk drive that incorporates a BPM disk, however, the data error is generated by a great error of controlling the recording timing. The data error inevitably increases or decreases the total number of data bits from the proper value. Hence, the conventional method of correcting data errors cannot be employed if the total number of data bits changes so.